A data center is a specialized facility that provides data serving and backup as well as other network-based services for subscribers and other entities. A data center in its most simple form may consist of a single facility that hosts all of the infrastructure equipment, such as networking and storage systems, servers, redundant power supplies, and environmental controls.
More sophisticated data centers may be provisioned for geographically dispersed organizations using subscriber support equipment located in various physical hosting facilities (sites). As a result, techniques have been developed to interconnect two more physical data centers to form a single, logical data center. One example layer two (L2) interconnect is an Ethernet virtual private network (EVPN) data center interconnect (DCI) through an intermediate network coupling multiple physical data centers.
An EVPN DCI is often used to extend two or more remote layer two (L2) customer networks of geographically separate data centers through an intermediate layer three (L3) network in a transparent manner, i.e., as if the intermediate L3 network does not exist. The EVPN transports L2 communications, such as Ethernet packets or “frames,” between customer networks via the intermediate network. In a typical configuration, provider edge (PE) network devices (e.g., routers and/or switches) coupled to the customer edge (CE) network devices of the customer networks define label switched paths (LSPs) (also referred to as pseudowires) within the provider network to carry encapsulated L2 communications as if these customer networks were directly attached to the same local area network (LAN). In some configurations, the PE network devices may also be connected by an IP infrastructure in which case IP/GRE tunneling or other IP tunneling can be used between the data centers.
With active-standby EVPN multi-homing, a customer edge device may be multi-homed to the EVPN by an Ethernet segment provided by multiple PE network devices. That is, the multiple PE network devices are coupled to the data center by separate access links that logically operate as a single Ethernet segment and, therefore, provide multi-homed connectivity to the EVPN for one or more customer networks within the local data center. In an active-standby configuration however, only one of the multiple PE network devices in the Ethernet segment operates as a designated forwarder (DF) with respect to each EVPN instance running over the Ethernet segment and forwards inbound Ethernet frames for that EVPN instance from the EVPN toward the multi-homed customer network using the Ethernet segment.